Exemplary circuit arrangements known from the prior art for controlling a light-emitting component E for the purposes of data transmission from the light-emitting component E (=so-called source) to a light-receiving component (=so-called sink) are shown in FIG. 5A to FIG. 5C.
Typically, a semiconductor laser or an electroluminescent diode is used as light-emitting component E, in particular as an optical transmitting element or as an optical source, for optical data transmission.
This semiconductor laser or this electroluminescent diode is, according to the prior art, for example supplied by an electronic driver circuit S1 (cf. FIG. 5a), S2 (cf. FIG. 5B) or S3 (cf. FIG. 5C) with the necessary operating voltage, the bias current and the modulation current for correct operation.
The driver circuit S1, S2, S3 can be constructed both as an integrated circuit (or IC=Integrated Circuit) and also discretely from individual components on a printed circuit board (or PCB=Printed Circuit Board).
In the example from the prior art shown in FIG. 5A, the light-emitting component E can be powered via a first current path I1 and additionally via a second current path I2. For this purpose in the first current path the current I1 flows from a DC voltage source Q via the light-emitting component E to a constant current source K1 for I1.
By switching to active or switching on the second current path I2 by means of a switch U which controls the current level of the light-emitting component E, the entire current Iges=I1+I2 flows through the light-emitting component E, otherwise the current I1. A constant current source K2 is provided for the power supply of the second current path I2.
The modulation of the light-emitting component E is thus effected in the form of current adjustment or current modulation, that is by temporally varying the current intensities flowing through the light-emitting component E between the values I1 and I1+I2.
The arrangement of switch U and dummy load R has the effect that at the switch U the same current always flows in relation to the node point assigned to the second current path I2, wherein when the second current path I2 is not switched to the light-emitting component E, the current I2 in the dummy load R is substantially converted into thermal energy which can, for example, be up to about fifty percent of the operating time of the light-emitting component; however, the current I2 is disadvantageously also present when this current I2 is no longer needed.
Furthermore, in the example from the prior art shown in FIG. 5A, the two constant current sources K1 and K2 are arranged in the high-frequency path (, i.e. not in the supply path) which necessarily involves parasitic capacitances. Also in the example from the prior art shown in FIG. 5A, an undesirable high voltage drop or a high saturation voltage necessarily occur.
In the second exemplary driver circuit S2 according to the prior art shown in FIG. 5B, when the second current path I2 is switched to active or switched on, the current I1+I2 flows through the light-emitting component E by means of the switch U which controls the current level, otherwise the current I1; however, the current I2 is disadvantageously also present when this current I2 is no longer needed.
The operating voltage of the light-emitting component E depends on the supply voltage supplied by the voltage source Q (=for example about three volts) and on the constant current source K1 or on the constant current sources K1, K2.
In the third exemplary driver circuit S3 according to the prior art shown in FIG. 5C, either the current I1+0.5I2 or the current I1−0.5I2, which results in a current difference of I2, flows through the light-emitting component E depending on the position of the switch U which controls the current level.
The arrangement of a (not obligatory) inductor L at which, for example, a voltage loss of about 0.5 volt occurs, is usually used to increase the impedance of the constant current source K1 at high frequencies and consequently makes it possible to use a constant current source K1 which does not have a high output impedance at high frequencies.
In addition to the previously described driver circuit S3, a driver circuit with inductor is also known from the prior art document U.S. Pat. No. 6,667,661 B1.
In the electronic driver circuit S3 shown in FIG. 5C, it is disadvantageously necessary to provide external components, that is, disposed outside the integrated circuit, such as a capacitor C.
As a result of the arrangement of inductor L and capacitor C, undesirable electromagnetic interference effects such as electromagnetic oscillations can furthermore occur. In this connection, for example, the prior art document U.S. Pat. No. 7,133,429 B2 is concerned with the problem of avoiding electromagnetic oscillations of a laser driver circuit with signal-amplified data transmission.
Another disadvantage of conventional circuit arrangements is their high voltage drop across the components in series with the light-emitting component. Particularly for applications in which only a small supply voltage is available, this conflicts with the aim of providing the highest possible operating voltage at the light-emitting component.
The technical formulation of the problem of providing a driver circuit for optical data transmission with low power drain is known, for example, from the prior art documents U.S. Pat. Nos. 6,965,722 B1 and 7,154,923 B2. However, the structure of the driver circuits described in these documents is very complex.
In addition, circuit arrangements known from the prior art disadvantageously have high output resistances (=real parts of the output impedances). This limits the speed, in particular for the transient ringing (or settling) or the circuit arrangement since the maximum switching frequency f behaves substantially reciprocally proportional to the product of the total capacitance C and total resistance R at the output of the controlling or driver circuit, wherein                the total capacitance C, for example, is substantially dominated by the parasitic capacitive effect of the light-emitting component and        the total resistance R is substantially given by the parallel circuit of the output resistance of the driver circuit and the input resistance of the light-emitting component.        
Finally, another technical problem of conventional circuit arrangements is a (too) low output voltage at the light-emitting component since the constant current source(s) require(s) a voltage (drop) of, for example, about 0.5 volt (a small voltage drop in the order of, for example, about 0.2 volt also occurs at the voltage source providing the supply voltage as long as this is a regulated voltage source).
Another small voltage drop in the order of, for example, about 0.1 volt occurs at the switching element U so that (too) little voltage occurs across the light-emitting component and therefore (too) little voltage is available at the light-emitting component.